I also have a simular problem with 1500+ chips, in a Tiger s2640 was working for about a year then XP went all buggy (probobly a virus) now the Bios only detects 1 CPU.
i cleaned all the connections and swapped over the CPU`S but still no differance. i`m not sure which processor has fallen over.
i don`t want to re-install XP with only one processor as i was told it won`t recognise and use the second processor until the OS is re-installed
Was also considering buying a new pair of CPU`s but after reading your experiances i don`t think i`ll bother. not sure how the Processors could be matched as they must comunicate to each other before using the Bus,
have read on another forum that two semperon`s wouldwork on the s2640 as you con`t find new MP`s any more
Please someone from AMD help.